Characterization of an absolute cryogenic radiometer as a standard detector for radiant-power measurements

Abstract

An active cavity radiometer of the electrical substitution type with a cone receiver that operates at 2-4 K has been developed for measuring radiant fluxes in the dynamic range of 20 nW to 100 microW within an uncertainty of +/-1% (2sigmalevel). It is a broadband absolute detector with a flat overall absorption efficiency that is >99% for radiation from the visible to long-wavelength IR. The system is designed based on thermal modeling and experimental measurements of concepts. It has been installed in the cryogenic chamber for low-background infrared radiation calibrations at the National Institute of Standards and Technology (NIST) for testing cryogenic blackbody sources, detectors, and optical components. Its time constant, responsivity, and nonequivalence error have been measured. They are in agreement with design predictions. Radiant power measurements of an amplitude-stabilized He-Ne laser beam with the radiometer and an industry standard photodiode detector, QED-200, have been intercompared and found to be in agreement. The intercomparison ratio of the measurements with the absolute cryogenic radiometer and QED-200 was 1.004 in the 75-100-microW range with an uncertainty of 0.5% (the 3sigma level).

Cryogenic blackbody calibrations attheNational Institute of Standards and Technology Low Background Infrared Calibration Facility

“…The average radius is corrected for thermal contraction as explained in Ref. [1]. The distance, S, between the blackbody aperture and the ACR limiting (precision) aperture is measured in two parts.…”

“…Uncertainties from systematic effects (here after called systematic uncertainties for simplicity) are of the following types for this experiment: 1) uncertainties in theoretical corrections applied to measured data such as the uncertainties associated with the diffraction corrections; 2) uncertainties in the measured values of parameters that remain constant during the calibration. Examples of such uncertainties are the parameters that characterize the ACR response [1] which do not change during the ACR power measurements. These uncertainties are TVpe B uncertainties according to Ref, [9] Subclause 3.3.3.…”

“…Us operating range for radiant power measurements is 20 nW to 100 ji.W with an expanded uncertainty of ± 1% (95% confidence level). The physical description of the ACR and its characterization as an absolute detector for radiant power measurements have been described in Ref, [1], The LBIR chamber is shown in Fig. 1.…”

Calibration of ultra-low infrared power at NIST

“…LBIR shares this standard with the user community through two primary methods: calibration of customer sources at our facility against our primary standards and by calibration of infrared testbeds at customer sites against our secondary standard transfer radiometers. The primary standard reference detector used is an absolute cryogenic radiometer (ACR), an electrical substitution device which provides a direct physical connection between the optical watt and the electrical watt [1][2][3]. The transfer radiometers contain our secondary standard detectors, which are Si:As blocked-impurity-band (BIB) detectors which have been calibrated against the ACR standards [4][5][6].…”

IR characterization of graphite black-coating for cryogenic detectors

“…The process by which these metal-blacks is deposited on thermal detectors, remains difficult somewhat black-paints deposition [8,9]. In addition, thermal sensors operated at cryogenic temperatures, allowed a large, highly absorptive black coating to be used without significantly increasing the time constant and the radiative coupling of the substrates to its surroundings is reduced [10,11]. The goal of this work is the development of new electrical substitution radiometer operating at room and cryogenic temperature, which serves as a standard for high optical power and energy measurements from 2.5 lm to 20 lm.…”